Developing modified k–ε turbulence models for neutral atmospheric boundary layer flow simulation using OpenFOAM

Accurate turbulence modeling is essential for simulation studies of urban physics. In this study, the comprehensive atmospheric boundary layer (ABL) model involving a variable model coefficient and an additional turbulent dissipation source term was implemented using the open-source software OpenFOAM. Combined with consistent inlet wind profiles and rough wall functions of different turbulence variables based on the aerodynamic roughness, the model maintained the horizontal homogeneity well. Then, a hybrid approach was introduced to consider buildings immersed in ABL flows, enabling automatic transformation of the turbulence model between the region around the buildings and the free flow region away from any building. Finally, the effects of applying different model forms to the airflow field around buildings were evaluated in detail through three-dimensional building cases representing six urban prototypes based on three wind tunnel databases. Our findings indicated that all modified k−ε models perform well in reproducing the flow data of the CEDVAL and Architectural Institute of Japan (AIJ) experiments consisting of a single building, an array of buildings, and an isolated high-rise building. However, the modified k−ε model with an additional correction term performed poorly in the database of Niigata Institute of Technology and the case of complex terrain and urban building configurations, because the correction term inhibited the generation of turbulent kinetic energy. In addition, from the comparison between the experimental data of all cases, the model with the original formulation of the coefficient performed the best in terms of prediction accuracy. The root mean square errors of the normalized velocity were 0.1250, 0.0879, 0.1145, 0.1350, and 0.1492 in different cases, which proved the reliability of this turbulence model.